Numerous capacitance-type measuring devices for making linear and angular displacement or position measurements have been developed wherein two members that are fixed relative to each other include respective capacitive electrodes that are capacitively coupled between the two support members and a third member is relatively movable between the two members to alter their capacitive coupling. The third member alters their capacitive coupling in a manner corresponding to the position of the third member relative to the first two members. The capacitive coupling affects one or more signals used to determine the position of the third member relative to the first two members. In a number of such measuring devices, the capacitive coupling, that is, the capacitance, is sensed by applying a plurality of temporally phase-shifted periodic signals to a plurality of capacitive transmitter electrodes on one of the first two members and measuring the relative phase shift of the one or more “summed” signals present on one or more capacitive receiver electrodes on the other one of the first two members, the relative phase shift of the one or miore “summed” signals resulting from the effect of the third member on the capacitive coupling between the electrodes first two members. Such capacitance-type measuring devices have a broad range of applications including motion control systems, measuring devices, and the like.
In a number of such capacitance-type measuring devices the third member includes one or more conductive electrodes that are effectively grounded to act as a “shield electrode” which affects or blocks the capacitive coupling between the first two members. For example, in U.S. Pat. No. 3,517,282, to Miller; U.S. Pat. No. 3,702,957, to Wolfendale; U.S. Pat. No. 3,732,553, to Hardway; U.S. Pat. No. 3,784,897, to Norrie; and U.S. Pat. No. 5,537,109, to Dowd, each of which is incorporated herein by reference for all of its relevant teachings, the third member includes one or more shield electrodes that are grounded to circuit or earth ground by electrical connection through a wire and/or wiper. Alternatively, U.S. Pat. No. 4,449,179, to Meyer, which is incorporated herein by reference for all of its relevant teachings, discloses grounding a “belt” shield electrode to earth ground (called “mass potential”) by electrical connection, or by suitable capacitive coupling to an earth ground member.
In a further alternative, U.S. Pat. No. 3,668,672, to Parnell, which is incorporated herein by reference for all of its relevant teachings, discloses connecting a shield electrode to a receiver electrode through an amplifier in such a way that the shield electrode is maintained at the same signal level as the receiving electrode. U.S. Pat. No. 6,492,911, to Netzer, incorporated herein by reference in its entirety, provides an overview that further discusses numerous configurations for such capacitance-type measuring devices and their disadvantages, including some of the configurations included in the foregoing incorporated references. The '911 patent further discloses and claims a configuration that capacitively senses a signal on an electrode on the third member and, after amplification, feeds back a capacitively coupled signal of the opposite polarity to the shield electrode in order to actively control its voltage or potential.